The present invention relates to heat exchangers employing the energy given off in the course of a liquid/vapor phase change or a vapor/liquid phase change of certain fluids and more particularly to such heat exchangers used in refrigeration equipment and/or heat pumps.
In machines of this type the heat exchangers are either constructed and designed for fulfilling a predetermined function either as an evaporator or as a condenser, or even designed to operate selectively as an evaporator and a condenser.
In case the heat exchanger is designed to be used exclusively as an evaporator it is underused since it is generally only half full and two-thirds full at best, in order to avoid "liquid knocking" in the compressor.
The only two-thirds or even half of the exchanger surface of the evaporator is therefore used when the flow of the fluid diminishes. Further, since the heat exchange is effected on small area cold surfaces, this contributes to the formation of frost in the case of air evaporators which of course is detrimental to efficiency.
In the case of condensers designed essentially to operate as such, for technological reasons the vapor reaching the condenser must be completely condensed at the exit. This requires over-dimensioning the condenser thereby increasing the cost of such a heat exchanger.
Finally, at the present time, the use of reversible refrigeration equipment requires that the exchangers be a compromise between evaporators and condensers, since they must operate equally as well as an evaporator or as a condenser, which accordingly in addition to the drawbacks specific to each type of exchanger referred to above, have low efficiencies.
In order to improve the heat exchange efficiency it has already been contemplated to line the inner wall of the heat exchanger tubes with a capillary structure to better distribute the liquid phase over the inner wall of such heat exchange tubes. The various solutions of this type which have been designed to now have not proved to be satisfactory in two important respects.
All contemplated capillary structures either do not provide capillarity over the entire inner surface of the tubes (this is particularly the case with woven or chained link metal fabric structures) or comprise baffles or obstacles slowing or retaining lubricating oil of the compressor of the system; some structures have both of these drawbacks.